Generally, a wind turbine includes a tower, a nacelle mounted on the tower, and a rotor coupled to the nacelle. The rotor typically includes a rotatable hub and a plurality of rotor blades coupled to and extending outwardly from the hub. Each rotor blade may be spaced about the hub so as to facilitate rotating the rotor to enable kinetic energy to be transferred from the wind into usable mechanical energy, and subsequently, electrical energy.
To properly orient the nacelle and the rotor blades relative to the direction of the wind, wind turbines typically include one or more yaw and pitch bearings. Yaw bearings permit rotation of the nacelle and are mounted between the tower and the nacelle. Pitch bearings permit rotation of the rotor blades and are mounted between the rotatable hub and a rotor blade. Typically, yaw and pitch bearings are slewing ring bearings that include an outer race and an inner race with a plurality of ball bearings between the races. In the case of yaw bearings, there may be a flat wear surface between washer-like raceways for supporting the loads while allowing the nacelle to yaw. One or more drive mechanisms are configured to drive the slewing ring bearings.
As wind turbines continue to increase in size, these slewing ring bearings must similarly increase in size due to increased loading. In order for a slewing ring bearing to withstand such loading, it must include various components that can adequately react to the increased loads. Thus, for example, two, three, or more rows of bearing balls may be included in a slewing ring bearing. However, such increase in the number and rows of bearing balls may be prohibitively expensive.
Additionally, increasing the size of a slewing ring bearing may result in increased load peaks. This is because the loads that the slewing ring bearing is subjected to are reacted over concentrated areas of the bearing. Load peaking describes load distribution, such as between the various balls of a bearing. A high load peak means that the load on the most highly loaded component, such as a bearing ball, is higher than the average load on all components. More efficient load transfer is thus obtained when load peaks are reduced. Thus, the slewing ring bearings of larger wind turbines must account for such increased load peaks.
Accordingly, a wind turbine with an improved slewing ring bearing would be desired in the art. For example, a slewing ring bearing that does not use ball or slide bearings yet provides improved distribution of loads and cost savings would be advantageous.